1. Field
This invention relates to image compression and reproduction, more particularly to image compression and reproduction in color reproduction devices.
2. Background
Image compression techniques allow image data to be transmitted or stored more efficiently, as the compressed image requires less space or lower bandwidth to be transmitted than the uncompressed image. Generally, color images can be compressed more efficiently in the luminance-chrominance color space (YCbCr) than in other color spaces, such as red-green-blue (RGB) or cyan-magenta-yellow-black (CMYK). However, output devices such as displays and printers usually require the image data to be in either RGB or CMYK format. This requires a process to convert between the compression color space and the output color space, referred to as color transformation.
Further a printer may also require that an image be half-toned in order to show more perceptible contrast levels than the print engine can actually print. This may also be true of displays with limited bit-depth, such as those used in personal digital assistants (PDAs). Some of those types of display only use 4 or 5 bits of display data per color, rather than the 8 bits used in typical large displays.
These processes can be done in several different ways. However, a method of image compression referred to as vector quantization (VQ) uses a look up table to compress and decompress the image. Similarly, both the color transformation and half-toning can use look up tables to manipulate the data appropriately.
Some work has taken advantage of these facts and proposed using half-toning and compression in a VQ encoder. However, no one has addressed this type of process in the decoder.